This invention relates to a fuel injector assembly, and more particularly to a high-pressure fuel injector assembly which includes a seat having a number of features for minimizing the formation of combustion chamber deposits on the seat. This invention also relates to the arrangement and manufacture of a fuel injector seat.
Fuel injectors are conventionally used to provide a measured flow of fuel into an internal combustion engine. In the case of direct injection systems, a high-pressure injector extends into the combustion chamber. Consequently, a downstream face of the fuel injector""s seat is prone to the formation of combustion chamber deposits. It is desirable to minimize this formation of deposits in order to maintain the intended operation of the fuel injector.
For the intended operation, it is critical for the seat to provide a sealing surface for engaging a displaceable closure member, e.g., a needle of a conventional fuel injector assembly. In a first position of the closure member relative to the seat, i.e., when the closure member contiguously engages the seat, fuel flow through the injector is prohibited. In a second position of the closure member relative to the seat, i.e., when the closure member is separated from the seat, fuel flow through the injector is permitted.
In order to provide the sealing surface, it is known to provide the seat with a conical portion having a desired included angle. Conventionally, grinding tools with a conical shape are used to grind the conical portion. It is also known that the quality of a surface finish is related to the grinding velocity. In the case of conical shape grinding tools, the grinding velocity decreases toward the apex of the tools.
In the case of fuel injector seats having a small orifice, the velocity of the grinding tool at the edge of the orifice is insufficient. Thus, conventional grinding operations cannot provide a selected finish on conventional conical portions.
The present invention overcomes the disadvantages of the seats in conventional fuel injectors, and provides a number of features for minimizing the formation of combustion chamber deposits.
According to the present invention, a transition portion is interposed between the conventional conical portion and the orifice, thus providing an additional volume in which the apex of the conventional grinding tool rotates.
However, excess sac volume, i.e., the volume of the fuel flow passage between the sealing band (i.e., the needle-to-seat seal) and the orifice, adversely affects the formation of combustion chamber deposits on the downstream seat. Thus, according to the present invention, the transition portion also minimizes sac volume.
Moreover, according to the present invention, a fuel injector seat is evaluated as to the necessity and configuration of a transition portion. This evaluation is based on different factors including orifice size and the included angle defined by the conical sealing portion.
Also, according to the present invention, an interface between the downstream face and the orifice is defined by a sharp edge. This facilitates dislodging combustion chamber deposits that may accumulate near the edge.
Additionally, according to the present invention, a fuel injector seat has a coating to control the formation of combustion chamber deposits in a first set of critical areas, and is uncoated in a second set of critical areas to facilitate the attachment and operation of the seat.
The present invention provides a fuel injector seat. The fuel injector seat comprises an upstream face; a downstream face spaced from the upstream face; a passage extending along an axis between the upstream face and the downstream face, the passage including an orifice portion proximate the downstream face; and a sharp edge at an interface between the orifice portion and the downstream face.
The present invention also provides a method of forming a fuel injector seat. The seat has an upstream face, a downstream face, and a passage extending along an axis between the upstream face and the downstream face. The method comprises forming within the passage an orifice portion proximate the downstream face; and forming a sharp edge at an interface between the orifice portion and the downstream face.
As it is used herein, the term xe2x80x9caxisxe2x80x9d is defined as a center line to which parts of a body or an area may be referred. This term is not limited to straight lines, but may also include curved lines or compound lines formed by a combination of curved and straight segments.
As it is used herein, the term xe2x80x9cratexe2x80x9d is defined as a value that describes the changes of a first quality relative to a second quality. For example, in the context of describing a volume, rate can refer to changes in the transverse cross-sectional area of the volume relative to changes in position along the axis of the volume. The term xe2x80x9cratexe2x80x9d is not limited to constant values, but may also include values that vary.
As it is used herein, the phrase xe2x80x9cincluded anglexe2x80x9d is defined as a measurement of the angular relationship between two segments of a body, when viewing a cross-section of the body in a plane including the axis of the body. Generally, the axis bifurcates the included angle.